Two Warm Neptunes transiting HIP 9618 revealed by TESS & Cheops

Abstract

HIP 9618 (HD 12572, TOI-1471, TIC 306263608) is a bright ($G=9.0$ mag) solar analogue. TESS photometry revealed the star to have two candidate planets with radii of $3.9\pm 0.044$ $R_{\oplus }$ (HIP 9618 b) and $3.343\pm 0.039$ $R_{\oplus }$ (HIP 9618 c). While the 20.77291 day period of HIP 9618 b was measured unambiguously, HIP 9618 c showed only two transits separated by a 680-day gap in the time series, leaving many possibilities for the period. To solve this issue, CHEOPS performed targeted photometry of period aliases to attempt to recover the true period of planet c, and successfully determined the true period to be 52.56349 d. High-resolution spectroscopy with HARPS-N, SOPHIE and CAFE revealed a mass of $10.0\pm 3.1M_{\oplus }$ for HIP 9618 b, which, according to our interior structure models, corresponds to a $6.8\pm 1.4\%$ gas fraction. HIP 9618 c appears to have a lower mass than HIP 9618 b, with a 3-sigma upper limit of $<18M_{\oplus }$. Follow-up and archival RV measurements also reveal a clear long-term trend which, when combined with imaging and astrometric information, reveal a low-mass companion ($0.08_{-0.05}^{+0.12}{M}_{\odot }$) orbiting at $26_{-11}^{+19}$ au. This detection makes HIP 9618 one of only five bright ($K<8$ mag) transiting multi-planet systems known to host a planet with $P>50$ d, opening the door for the atmospheric characterisation of warm ($T_{\mathrm{eq}}<750$ K) sub-Neptunes.

arXiv comment19 pages, 16 figures, 9 tables. Accepted at MNRAS. CHEOPS, RV and ground-based photometric data is available on CDS at https://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/523/3069

References in corpus (79)

• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Transiting Exoplanet Survey Satellite
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars
• Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 20945
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• Las Cumbres Observatory Global Telescope Network
• Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
• The Revised TESS Input Catalog and Candidate Target List
• Gaia Early Data Release 3: Parallax bias versus magnitude, colour, and position
• The NASA Exoplanet Archive: Data and Tools for Exoplanet Research
• Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
• Understanding the Mass-Radius Relation for Sub-Neptunes: Radius as a Proxy for Composition
• AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves
• AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves (Expanded Edition)
• A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
• Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators
• The TESS Objects of Interest Catalog from the TESS Prime Mission
• HAT-P-16b: A 4 Mj Planet Transiting A Bright Star On An Eccentric Orbit
• Three regimes of extrasolar planets inferred from host star metallicities
• PandExo: A Community Tool for Transiting Exoplanet Science with JWST & HST
• Parametrizing the exoplanet eccentricity distribution with the Beta distribution
• Kepler Data Validation I -- Architecture, Diagnostic Tests, and Data Products for Vetting Transiting Planet Candidates
• Almost All of Kepler's Multiple Planet Candidates are Planets
• Transmission Spectra of Three-Dimensional Hot Jupiter Model Atmospheres
• Understanding The Effects Of Stellar Multiplicity On The Derived Planet Radii From Transit Surveys: Implications for Kepler, K2, and TESS
• The CHEOPS mission
• Atmospheric Escape and the Evolution of Close-in Exoplanets
• The Kepler Follow-Up Observation Program. I. A Catalog of Companions to Kepler Stars from High-Resolution Imaging
• The orbital eccentricity of small planet systems
• Kepler Data Validation II -- Transit Model Fitting and Multiple-Planet Search
• Real-time processing of the imaging data from the network of Las Cumbres Observatory Telescopes using BANZAI
• WASP-3b: a strongly-irradiated transiting gas-giant planet
• SOAR TESS Survey. I: Sculpting of TESS planetary systems by stellar companions
• Misaligned spin-orbit in the XO-3 planetary system?
• A generalized bayesian inference method for constraining the interiors of super Earths and sub-Neptunes
• exoplanet: Gradient-based probabilistic inference for exoplanet data & other astronomical time series
• A Guide to Realistic Uncertainties on Fundamental Properties of Solar-Type Exoplanet Host Stars
• Six transiting planets and a chain of Laplace resonances in TOI-178
• Ten years of speckle interferometry at SOAR
• Identification of carbon dioxide in an exoplanet atmosphere
• Bayesian distances and extinctions for giants observed by Kepler and APOGEE
• Atomic data for the Gaia-ESO Survey
• PALM-3000: Exoplanet Adaptive Optics for the 5-meter Hale Telescope
• AQUA: A Collection of H${}_2$O Equations of State for Planetary Models
• From stellar nebula to planets: the refractory components
• SOPHIE+: First results of an octagonal-section fiber for high-precision radial velocity measurements
• TESS Spots a Compact System of Super-Earths around the Naked-Eye Star HR 858
• Expected performances of the Characterising Exoplanet Satellite (CHEOPS) III. Data reduction pipeline: architecture and simulated performances
• A new method to compute limb-darkening coefficients for stellar atmosphere models with spherical symmetry: the space missions TESS, Kepler, Corot, and MOST
• A new ab initio equation of state of hcp-Fe and its implication on the interior structure and mass-radius relations of rocky super-Earths
• Determining stellar parameters of asteroseismic targets: going beyond the use of scaling relations
• orvara: An Efficient Code to Fit Orbits using Radial Velocity, Absolute, and/or Relative Astrometry
• Speckle Observations of TESS Exoplanet Host Stars. II. Stellar Companions at 1-1000 AU and Implications for Small Planet Detection
• Gas composition of main volatile elements in protoplanetary discs and its implication for planet formation
• Analysis of Early Science observations with the CHaracterising ExOPlanets Satellite (CHEOPS) using pycheops
• The Densities of Planets in Multiple Stellar Systems
• WASP-186 and WASP-187: two hot Jupiters discovered by SuperWASP and SOPHIE with additional observations by TESS
• CAFE: Calar Alto Fiber-fed Echelle spectrograph
• Gaia Search for stellar Companions of TESS Objects of Interest
• Unresolved Binary Exoplanet Host Stars Fit as Single Stars: Effects on the Stellar Parameters
• Uncovering the true periods of the young sub-Neptunes orbiting TOI-2076
• A Possible Alignment Between the Orbits of Planetary Systems and their Visual Binary Companions
• TESS-Keck Survey IX: Masses of Three Sub-Neptunes Orbiting HD 191939 and the Discovery of a Warm Jovian Plus a Distant Sub-Stellar Companion
• Gaia Search for stellar Companions of TESS Objects of Interest II
• The SOPHIE search for northern extrasolar planets. X. Detection and characterization of giant planets by the dozen
• HD 191939 revisited: New and refined planet mass determinations, and a new planet in the habitable zone
• Results from The COPAINS Pilot Survey: four new brown dwarfs and a high companion detection rate for accelerating stars
• Two long-period transiting exoplanets on eccentric orbits: NGTS-20 b (TOI-5152 b) and TOI-5153 b
• Information content of JWST-NIRSPEC transmission spectra of warm Neptunes
• Detecting Unresolved Binaries in TESS Data with Speckle Imaging
• HD 191939: Three Sub-Neptunes Transiting a Sun-like Star Only 54 pc Away
• TOI-5678 b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS
• HD 28109 hosts a trio of transiting Neptunian planets including a near-resonant pair, confirmed by ASTEP from Antarctica
• Transit timing variations of AU Microscopii b and c
• The HD 93963 A transiting system: A 1.04d super-Earth and a 3.65 d sub-Neptune discovered by TESS and CHEOPS
• CAFE2: an upgrade to the CAFE high-resolution spectrograph. Commissioning results and new public pipeline
• Refined parameters of the HD 22946 planetary system and the true orbital period of planet d
• TESS and CHEOPS Discover Two Warm Sub-Neptunes Transiting the Bright K-dwarf HD 15906

Cited by in corpus (9)

• A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067
• TOI-5678 b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS
• Refined parameters of the HD 22946 planetary system and the true orbital period of planet d
• TESS and CHEOPS Discover Two Warm Sub-Neptunes Transiting the Bright K-dwarf HD 15906
• The "Drake equation" of exomoons -- a cascade of formation, stability and detection
• Two neighbours of the ultra-short-period Earth-sized planet K2-157 b in the warm Neptunian savanna
• HIP 41378 observed by CHEOPS: Where is planet d?
• A Cool Earth-sized Planet Candidate Transiting a Tenth Magnitude K-dwarf From K2
• Discovery of a multi-planetary system orbiting the aged Sun-like star HD 224018